This uses grcov internally to generate the HTML report. We use grcov
instead of, say, lcov, because grcov actually generates accessible
pages.
We use the gnome-build-meta:core-nightly container image. It doesn't
contain grcov by default, but we download the binary from its github
page. We can change this later to build a custom container image for
gnome-calendar's own CI.
This will publish the report on
https://gnome.pages.gitlab.gnome.org/gnome-calendar/coverage/
